Active flow control by harmonic blowing through a slot is investigated for a modified NACA643-618 airfoil at a chord Reynolds number of Re=300,000 and for 15 degrees angle of attack. A direct simulation of the uncontrolled flow serves as a reference for hybrid simulations using a one-equation renormalization group turbulence model. Because of their lower computational expense, two-dimensional hybrid calculations are employed for active flow control parameter studies. Downstream harmonic blowing through a spanwise slot is investigated. For a blowing ratio of 0.1 the control is ineffective. For blowing ratios and dimensionless forcing frequencies between one and two the actuation results in vortex shedding of the separated boundary layer and a moderate rise in lift.